Beyond Smooching: The Science of Mistletoe

While waiting under the mistletoe for that kiss, you might look up and think about the other important functions of mistletoe. Ira Flatow, host of Science Friday, discusses mistletoe's non-holiday life with Madeleine Brand.

MADELEINE BRAND, host:

This is DAY TO DAY. I'm Madeleine Brand.

While you're standing under the mistletoe this year waiting for that lucky person, you might look up and contemplate the many important functions that mistletoe serves besides attracting a holiday smooch. Here to fill us in is Ira Flatow, host of NPR's "Science Friday" and a regular Thursday contributor to DAY TO DAY.

Hi, Ira.

IRA FLATOW reporting:

Hi, there.

BRAND: So are you saying mistletoe actually has a purpose in nature other than the mating rituals of homo sapiens?

FLATOW: Absolutely. This is really an interesting plant. In nature, some butterflies and birds and insects really could not survive without it. The name itself, mistletoe, really explains its niche in nature. Mistletoe comes from the Anglo-Saxon `misteltan.' And `mistel' in Anxlo-Saxon means `dung' and `tan' means `twig,' so mistletoe literally means `dung on a twig'...

BRAND: Wow, not--yeah.

FLATOW: ...which is not quite what you're thinking of when you're standing under it, right?

BRAND: Right.

FLATOW: But it really is an accurate description in describing how the birds help spread mistletoe seeds in their droppings, and they rely on the berries for food. For example, the silk flycatcher--I knew you were going to ask about that--which lives in the Desert South and Southwest, relies almost exclusively on white mistletoe seeds for food in the winter. But you also have bluebirds and grouse and mourning doves and robins and pigeons--they all eat the mistletoe seeds. And the trees also serve as homes for the spotted owl, hawks and other raptors. So it really is ubiquitous.

BRAND: So how common is it?

FLATOW: It's common all over the world and common very well spread around this country. There are 1,300 species of mistletoe, but the one that you may be standing under probably comes from one native to the US. That's the American mistletoe that's found everywhere from New Jersey to Florida. It stretches into Texas. It has a kissing cousin, so to speak, the dwarf mistletoe, which is found in central Canada and into southern Alaska.

And what's interesting also about the mistletoe is its life cycle, because you have these seeds that can burst out of the seed coverings into the tree, and these seeds spread long tentacle roots which grab the wood and they literally suck the sap out of the tree. It's almost like a parasite. In fact, the American mistletoe's scientific name means `thief of the tree' in Greek. And they grow into these masses of thick, branching stems which, because of the way they look, have been given the name witch's broom or a basket on high, as the Navajo call it.

BRAND: And, Ira, you said a whole bunch of animals are reliant on mistletoe, one of them being butterflies.

FLATOW: Mm-hmm. Yeah. Scientists say that three kinds of butterfly depend on mistletoe and, one, the great purple hairstreak, according to John Opler at Colorado State University, is the only butterfly in the US that feeds on American mistletoe, the one we use for Christmas.

But you have bees that rely on mistletoe for nectar and pollen, and there are other insects that eat the shoots, the fruits and the seeds. So mistletoe are home for birds and they're also food for birds.

BRAND: And what about bigger animals?

FLATOW: Well, you have elk and deer and cattle that chew the leaves and berries in the winter when snow covers the ground. But this is a habit that should not be adopted by people, because mistletoe is highly toxic to people. So not only do you not want to be chewing on it, you want to make sure that when you bring some home or you go to someone's home for the evening or on Christmas, make sure that the kids and the pets, the family pets, stay away from it, because you know how kids and animals like to put things in their mouths; it's just not a good plant to chew on.

BRAND: But a good one to kiss under.

FLATOW: Mm-hmm.

BRAND: Ira Flatow, host of "Science Friday" and a regular Thursday contributor to DAY TO DAY.

Thanks, Ira.

FLATOW: Happy holidays.

(Soundbite of "The Christmas Song")

Mr. NAT "KING" COLE: (Singing) A turkey and some mistletoe help to make the season bright...

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